1. Field of the Invention
This invention relates to the control of fine particulate by sonic agglomeration and more particularly to a system for maintaining high resonance during the sonic agglomeration of the particulate.
2. Description of the Prior Art
It is known that conventional agglomerators can operate at a power conversion efficiency (.beta.Na) of approximately 0.03-0.14. These values are the product of sound source efficiency (Na) and the chamber resonance enhancement factor (.beta.).
These low power conversion efficiency (.beta.Na) values suggest that:
(1) no resonance exists in the chamber of the system; and
(2) poor coupling exists between the sound source and the chamber. Direct radiation from the sound source should produce a higher (.beta.Na).
The measurement of (.beta.Na) for the agglomerator disclosed in the patent and publication, respectively, to St. Clair (U.S. Pat. No. 2,215,484 and the publication by St. Clair, H. W., entitled "An Electromagnetic Sound Generator for Producing Intense High Frequency Sound", and appearing in Rev. Sci. Instruments, May, 1941, pages (250-255) shows that while a (.beta.) of five (5) could be obtained, the efficiency of the St. Clair sound source is so poor that the net (.beta.Na) is much less than one (1). In addition, the resonant piston sound generator disclosed in this patent is not suitable for scaling up to dimensions required for driving an industrial sized agglomeration chamber.
Chamber resonance is obtained in the St. Clair agglomerator by adjusting the chamber length. The St. Clair agglomerator uses a phase shifting network and analog feedback to maintain the sound source, not the chamber, in resonance. This method of maintaining resonance is inadequate because the frequency is fixed by the length of the sound producing cylinder and cannot be varied. Moreover, the chamber design used by St. Clair is based on a one-dimensional propagating wave analysis.
An attempt was made in the past to develop an agglomerator using as a sound source a whistle which has a cylindrical cavity maintained in resonance by air flowing from a nozzle. It is extremly difficult to maintain resonance with such a sound source because minor changes in air pressure or changes in the position of nearby reflecting surfaces are sufficient to destroy the resonance. This experience provided recognition of the need for a control effective enough to maintain resonance.
Analog control of a treating chamber is disclosed in the patent to Coleman et al (U.S. Pat. No. 2,949,166). An analog signal generator in this patent is controlled by feedback from the chamber. A drawback to this control system is that it cannot distinguish the optimum resonant frequency for the chamber from the many other closely spaced resonant modes that exist within a typical industrial sized agglomeration chamber. If the analog signal generator momentarily falls out of resonance, there is a strong possibility that it will lock onto a non-optimum frequency. Furthermore, in order for the feedback mechanism to remain stable, gain of the analog signal generator must be compromised and it will not achieve the frequency where resonant enhancement of the sound within the chamber is maximized.